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Drifting Continents Did Pangaea Exist? The Theory of Continental Drift A German scientist named Alfred Wegener formed the hypothesis that the continents had moved! He proposed that all the continents had once been joined together in a single landmass and have since drifted apart. The Theory of Continental Drift Wegener’s idea that the continents slowly moved over the earth became known as continental drift. Unfortunately Wegener could not provide a satisfactory explanation for the force that pushed or pull the continents. Therefore most geologists rejected his idea. Evidence of Continental Drift Evidence from landforms: Mountain ranges and other features on the continents provided evidence for continental drift. Mountain ranges in South Africa line up with mountain ranges in Argentina (South America). Evidence for Continental Drift Evidence from fossils A fossil is any trace of an ancient organism that has been preserved in rock. Glossopteris fossils have been found in rocks in Africa, South America, Australia, India, and Antarctica. Evidence for Continental Drift Evidence from climate Fossils of tropical plants have been found too far north or south to have survived. Glacier deposits are found too close to the equator. These clues provide evidence that continental drift really happened. Rejection!! Even with the evidence, most scientists rejected Alfred Wegener’s theory for about a half a century, from the 1920s to the 1960s. Let’s See What Wegner Thought Really Happened! http://www.suu.edu/faculty/colberg/Hazard s/PlateTectonics/18_Pangaea.html http://www.exploratorium.edu/origins/antar ctica/ideas/gondwana2.html Energy is constantly on the move! The movement of energy from warmer object to a cooler object is called a heat transfer There are three types of heat transfer: radiation, conduction, and convection. Radiation Radiation is the transfer of energy through empty space. Heat transfer by radiation takes place with no direct contact between a heat source and an object. Conduction Heat transfer by direct contact of particles is called conduction. When your hands touches a metal spoon sitting in a boiling pot of soup, the heat from the bottom of the pot is transferred to your hand by conduction. Conduction Convection Convection is the transfer of heat by the movement of a heated fluid. Convection deals with density. Density is the measure of how much mass is there in a certain volume of a substance. Convection When a liquid or gas is heated, the particles move faster and the density decreases. As the fluid becomes cooler, its density increases. As density increases, the fluid sinks. Heat Rises!! Convection The heating and cooling of the fluid, changes in the fluid’s density, and the force of gravity combine to set convection currents in motion. Without heat, convection currents will eventually come to a stop. Convection Currents in the Mantle The heat source for these convection currents in the mantle comes from the heat of the Earth’s core. Convection in the Earth’s Mantle The crust “floats” on the mantle, just like Cheerios float on the surface of milk. The convection currents in Earth’s mantle cause the crust to move ever so slightly, therefore, allowing continents to drift. Plate Tectonics Based on the knowledge that the lithospheric plates float on the asthenosphere, the theory of plate tectonics was developed. Radiation, Conduction, and Convection